Work, Energy and Power Class 11

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Work Energy and Power Class 11

With exams around the corner, it is always helpful to have notes to refer to. Work, energy and strength are the most commonly used concepts which are present in Physics Class 11. They are probably the first thing you have learned in your science class. Work and electricity are synonymous with each other. If you want to become a physicist then your basics should be strong. Worry not! In this blog, we will study more about the idea of work, energy and power class 11. 

Must Read: Class 11 Gravitation Notes


Let us have a quick overview of some of the important basics of work, energy and power class 11 chapter. Through this, we will understand what is work, energy and power. You can check it out here:

Definition of Work

Definition When a force applied to an object moves that object, then it is called as Work
Formula W = F × d
SI Unit The SI unit of work is labelled as joule (J). 

Definition of Energy

Definition Energy is defined as the capacity to do work.
Formula P.E. = mgh
Si Unit The SI unit of energy is called as joules (J)

Definition of Power

Definition The rate at which work is done i.e. the energy converted can be defined as Power. 
Formula P = W/t
SI Unit The SI unit of power is called watt (W).

Definition of Work  

Let us understand the definition of work in the chapter work, energy and power class 11. Work is said to be achieved as the body or entity moves by the use of external force. Work can be interpreted as an action requiring motion and power in the direction of the applied force. 

W = F × d

For example, a force of 30 Newtons (N) that moves the object 3 metres in the same direction as the force does 90 Joules (J) of work.

The SI unit of work is labelled as joule (J). 


An object is pulled across the surface by a 100 N force which is acting parallel to the surface horizontally. Calculate the amount of work done which is performed by the force in the moving object through a distance of 8 m


Given, F = 100 N
d = 8 m
Since F and d are present in the same direction,
θ = 0, [θ is the angle of the force to the direction of movement]W = F Cos θ
= 100 x 8 x Cos 0
= 800 J [Since Cos 0 = 1]

Definition of Energy

Next in work, energy and power class 11 we have the definition of energy. Energy is defined as the ability to do a task. Energy cannot be produced or lost. It can only be converted from one type to the next. The Energy Unit is much like the Job Unit, i.e. It’s Joules. The presence of energy is in various products, therefore the various types of energies are vast. 

P.E. = mgh

Most forms of energy seem to be either kinetic or potential. The energy of action is defined as kinetic energy, while the potential energy is the energy contained in the body and determined by the amount of work performed.

The SI unit of energy is called joules (J).

Kinetic Energy  

Energy generated by the body because of its motion is regarded as the kinetic energy of the body. Kinetic energy acquired by moving the body is equivalent to average work performed by the body just before heading to rest. 

Kinetic energy = 1/2 mv2 

Potential Energy  

Energy which is generated by the body as a consequence of its position or state is defined as Potential Energy. Some of the examples for potential energy are energies like gravitational potential energy, electrostatic potential energy, elastic potential energy etc.

Definition of Power

Moving forward in work, energy and power class 11, we will examine the meaning of power. Power is a physical phenomenon that has a variety of different interpretations, depending on the situation and the knowledge accessible. The rate at which work is performed is known as work. This is the measure of energy consumed per unit of time.

P = W/t
P = Power
W = Work done
T = Time taken

Definition of Work Energy Theorem

The work done on a body by applying force is equal to the change in kinetic energy of the body. This is defined as Work-Energy Theorem. 

Law on the Conservation of Energy 

The Law of Conservation of Energy states that the total energy of an isolated system does not alter or change. Energy can be converted from one form to another, but the total energy that is present in an independent entity remains unchanged. 

Energy cannot be Produced or Lost

In addition to mechanical energy, energy can manifest itself in many other ways. Any of these forms include: thermal energy, electrical energy, chemical energy, visual light energy, nuclear energy, etc. 

Mass and Energy Equivalence 

Next on work, energy and power class 11, we have the equivalence of mass and energy. Einstein says that energy and mass are synonymous. That is, mass can be transformed into energy, and energy can be transformed into mass.


Collision is characterised as an isolated occurrence in which two or more colliding objects exercise relatively strong forces over a relatively short period of time. The collision between particles has been widely categorised into two forms which can be defined as: 

  • Elastic Collisions
  • Inelastic Collisions

Elastic Collisions 

A collision between two particles or bodies is considered to be elastic if both the linear momentum and the kinetic energy of the system are preserved is said to be known as Elastic Collisions. Ex: a collision between atomic particles, electrons, marble balls and billiard balls.

Inelastic Collisions 

A collision is considered to be an inelastic collision if the linear momentum of the system is retained, but the kinetic energy is not maintained.

Example Questions

Here are a few important example questions to make you thorough in work, energy and power class 11. 

  1. Comets are passing around the sun in extremely elliptical orbits. The gravitational force on the comet due to the sun is not natural to the velocity of the comet in general. Yet the function of gravitational force over a full orbit of the comet is negligible. Why? 

Ans. The force of gravity is defined as a conservative force. The work undertaken by conservative forces on a closed path is zero. Thus, for a full orbit of the comet, the work undertaken by the gravitational force is zero.

  1. A molecule with a speed of 300 m s-1 hits the wall of the container at an angle 40∘ with the normal and rebounds with the same speed. During the collision is the momentum conserved?

Ans. The collision can be defined as an elastic collision. Whether the collision is an elastic or an inelastic collision, the momentum is conserved. The molecule travels at a speed of 300 m/s and strikes the wall and rebounds with the same speed. Therefore, the rebound velocity is zero. During the collision, the total kinetic energy is conserved.

Explore: Class 11 Oscillations Notes

Thus, this was all about Work, Energy and Power  Class 11. We hope that our notes help you and wish you all the best. Check out Leverage Edu for more Class 11 notes.

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